In general, a color reproduction range (also referred to as a “color space”, a “color gamut”, or a “color purity”) of display apparatuses, printing apparatuses, image pickup apparatuses, and the like is different by the model. In addition, for color television apparatuses, a color reproduction range of inputted video signals is different by the employed television system. For this reason, conventionally, color conversion processing of a variety of types is performed when generating output data based on inputted data, in order to output colors as accurately as possible to the inputted data regardless of the color reproduction range. For example, when performing HDTV (High Definition Television) broadcasting using a color television apparatus that employs a liquid crystal panel, signals in a standard specified by ITU-R (International Telecommunication Union Radiocommunications Sector) BT.709 (hereinafter referred to as the “HDTV standard”) are supplied to the color television apparatus from an external signal source. In this case, the signals supplied to the color television apparatus from the external signal source are RGB signals. In the color television apparatus, mapping (matching) processing of a color gamut of an RGB signal supplied from the signal source to a color gamut in the liquid crystal panel that constitutes the color television apparatus (hereinafter referred to as the “color gamut conversion processing”) is performed. Then, by applying a voltage corresponding to a value of each color included in the RGB signal obtained through the color gamut conversion processing to the liquid crystal layer, color is displayed in a display portion of the liquid crystal panel as accurately as possible to color represented by the RGB signal supplied from the signal source. The following describes the color gamut conversion processing performed in the color television apparatus in detail.
FIG. 8 is a table showing chromaticity coordinate values (coordinate values on an xy chromaticity diagram) of primary colors in the HDTV standard and chromaticity coordinate values of primary colors in a liquid crystal panel that constitutes a display apparatus (color television apparatus). Referring to FIG. 8, for example, it can be seen that “the chromaticity coordinate (x, y) for R (red) is (0.6400, 0.3300) in the HDTV standard”. In this case, by performing normalization based on information related to the HDTV standard represented by a reference numeral 91 in FIG. 8 such that brightness Y of W (white) in the XYZ color space is 1, a following equation (1) expressing a relation between an RGB value and an XYZ value can be obtained. It should be noted that X, Y, and Z are tristimulus values in an XYZ colorimetric system.
                    [                  Equation          ⁢                                          ⁢          1                ]                                                                      (                                                    X                                                                    Y                                                                    Z                                              )                =                              (                                                                                0.4124                    ,                                                                                        0.3576                    ,                                                                    0.1805                                                                                                  0.2126                    ,                                                                                        0.7152                    ,                                                                    0.0722                                                                                                  0.0193                    ,                                                                                        0.1192                    ,                                                                    0.9505                                                      )                    ⁢                                    (                                                                    R                                                                                        G                                                                                        B                                                              )                        HDTV                                              (        1        )            
Similarly, a following equation (2) expressing a relation between the RGB value and the XYZ value based on information related to the liquid crystal panel represented by a reference numeral 92 in FIG. 8 can be obtained as listed below.
                    [                  Equation          ⁢                                          ⁢          2                ]                                                                      (                                                    X                                                                    Y                                                                    Z                                              )                =                              (                                                                                0.4091                    ,                                                                                        0.3101                    ,                                                                    0.2840                                                                                                  0.2071                    ,                                                                                        0.6906                    ,                                                                    0.1023                                                                                                  0.0136                    ,                                                                                        0.0913                    ,                                                                    1.5085                                                      )                    ⁢                                    (                                                                    R                                                                                        G                                                                                        B                                                              )                        panel                                              (        2        )            
Furthermore, where “right side in the equation (1)=right side in the equation (2)”, a following equation (3) can be obtained as listed below.
                    [                  Equation          ⁢                                          ⁢          3                ]                                                                                  (                                                            R                                                                              G                                                                              B                                                      )                    panel                =                              (                                                                                1.0002                    ,                                                                                        0.1021                    ,                                                                                        -                    0.0056                                                                                                                    0.0075                    ,                                                                                        1.0024                    ,                                                                    0.0130                                                                                                  0.0033                    ,                                                                                        0.0174                    ,                                                                    0.6294                                                      )                    ⁢                                    (                                                                    R                                                                                        G                                                                                        B                                                              )                        HDTV                                              (        3        )            
In this case, the equation (3) is to obtain values of the respective RGB colors corresponding to voltage values to be applied to a liquid crystal layer in the liquid crystal panel from the RGB signals in the HDTV standard supplied from the signal source. Specifically, as shown in FIG. 9, an RGB signal RGBin in the HDTV standard is inputted into a display apparatus (color television apparatus) 9 from a signal source 93, and the RGB signal RGBin is converted based on the equation (3) by a color gamut conversion processor 94. Then, an RGB signal RGBout obtained through the conversion processing by the color gamut conversion processor 94 is supplied to a liquid crystal panel 95. In this manner, color accurate to the color represented by the RGB signal RGBin supplied from the signal source 93 is displayed in a display portion of the liquid crystal panel 95.
Further, conventionally, there is known white balance processing for correcting colors such that white color is displayed correctly regardless of a color temperature of a light source. In white balance processing, a value of each color of RGB is multiplied by a predetermined gain so as to suppress a disturbance in the balance among the RGB colors due to a difference between light sources.
It should be noted that, in relation to the present invention, the following prior art references are known. Japanese Unexamined Patent Application Publication No. H04-291591 discloses an invention relating to a color display apparatus capable of reproducing colors of any of inputted video signals having a plurality of different color reproduction ranges from each other without a color reproduction error. Japanese Unexamined Patent Application Publication No. 2008-78737 discloses a technique of preventing a color gamut of an image output device from being unnecessarily wide by correcting brightness or luminance. Japanese Unexamined Patent Application Publication No. 2008-86029 discloses a method of acquiring desired color reproduction by utilizing a standard color space with an extended color gamut.